CH622039A5 - - Google Patents

Description

The present invention aims to remedy the above drawbacks.

The dobby according to the invention, in which each element associated with a frame or group of heald frames comprises a half-pendulum animated by a reciprocating movement, a balance carried at articulation by the latter and whose ends are equipped with coupling hooks, this balance being actuated by two crosspieces carried by oscillating supports and common to all the elements of the dobby, and two retaining hooks intended to cooperate selectively with the coupling hooks, each of these retaining hooks comprising, on the one hand, a first part or main part articulated to the frame and which carries the hooking spout, on the other hand, a second part or selection part articulated to the first, connected to the latter by a spring and stop system, and receiving the action of the armor mechanism, the whole so that this mechanism can prepare the selection of the balance considered by moving the second part of one of the retaining hooks beforethe corresponding towing hook has not come to the end of the recoil stroke, this retaining hook being erased in the manner of a pawl when said towing hook passes to hang behind it, while at each of the two rows of dobby retaining hooks is associated a locking bar driven back and forth and which cooperates with the first part of each hook of the row considered to lock this part either in the erased position for which the retaining hook considered cannot retain the corresponding towing hook, that is to say on the contrary to the engaged position for which this first part hooks to said towing hook, which bars alternately release the first parts of the retaining hooks for the selection, one during even strokes, the other during odd strokes, is characterized in that, in each element, the second parts or selection parts of the two retaining hooks are activated during selection by a single member associated with the armor mechanism.

Each of these control members is advantageously produced in the form of a pusher, the head of which is guided substantially in the plane of symmetry of the two hooks, while its tail is moved transversely to this plane by the armor mechanism so as to selectively receiving the action of at least one thrust member common to all the elements and driven back and forth in synchronism with the operation of the loom.

In the case of a reverse dobby, there are provided two thrust members suitably out of phase with each other and these members are produced in the form of two nested combs, arranged laterally with respect to the row of pushers (therefore above or below this row), their teeth being oriented towards them so as to cooperate selectively with corresponding teeth provided on said pushers. As for the armor mechanism ensuring the selection of the pushers, it can be established in the known manner by means of reading needles coupled to them and cooperating with a strip of perforated paper.

The attached drawing shows by way of example a dobby according to the invention:

fig. 1 is a cross section of this dobby; so as not to complicate the drawing, it has been assumed that the other elements thereof are in front of the plane of the figure;

fig. 2 is a partial cross section on a larger scale showing a pusher and its control mechanism;

fig. 3 is a partial plan view illustrating the arrangement of the pushers and their actuation combs;

fig. 4 and 5 show two positions of the essential parts of an element of the dobby during operation;

fig. 6 illustrates the control of the combs by means of a desmodromic cam;

fig. 7 reproduces fig. 2, but indicating an electromagnetic control mode for the selection of the pushers;

fig. 8 is a graph intended to show the overall functioning of the dobby.

The dobby according to the invention, an assembly of which has been shown in FIG. 1, comprises for the latter, in the conventional manner, a control lever or half-balance 1 mounted on a fixed bransversal shaft 2 common to all the elements, this half-balance actuating a connecting rod 3 suitably connected to a heald frame of the profession or a group of such executives who must function identically. The connection mechanism has not been detailed, which may include, in the usual manner, an amplitude adjustment lever and a system of cables and return pulleys. The half-pendulum 1, provided approximately in the shape of an arc of a circle, carries at the end a balance 4, that is to say a kind of double lever with aligned arms of equal length, which, for its part, is articulated by its middle in 5. Each of the ends of the balance 4 pivotally supports a coupling hook 6a, respectively 6b, pivoted in 7a, respectively 7b, and the heel of which has a flat bearing surface 8a, respectively 8b. It is, on the other hand, provided in the dobby two crosspieces 9a, 9b common to all the elements and the assembly of which is supported by two end flanges 10 mounted for rotation on the fixed frame (not shown) of this dobby by means of shaft ends such as 11. A suitable mechanism, such as a connecting rod 12 coupled, on the one hand, at 13 to the flange 10 considered, on the other hand, at 14 to an eccentric 15 mounted on a shaft 16 driven at the rate of one revolution for two strokes of the loom, moves the cross members 9a, 9b back and forth so that they come to bear against the bearing surfaces 8a, 8b of the coupling hooks 6a, 6b by positively orienting the latter and by normally oscillating the balance 4 of the element considered when these hooks are free. Finally, opposite the coupling hooks 6a, 6b, two retaining hooks are provided, each comprising a first part or main part 17a, respectively 17b mounted idly on a common shaft 18a, respectively 18b, these retaining hooks being suitable for selectively cooperate with the aforementioned coupling hooks.

The construction described so far is absolutely classic. We will very briefly recall its operation: when the two retaining hooks (or more precisely their main parts) 17a, 17b are released (position in fig. 2), the balance 4 can oscillate freely around its axis 5 under the effect of the crosspieces 9a, 9b and the half-balance 1 is not actuated. But if, when one is in the advanced position of a towing hook, 6a for example, one engages the corresponding retaining hook 17a, during the advance of the opposite cross member 9b the balance 4 cannot oscillate

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freely and, consequently, its axis 5 advances by advancing the half-balance 1.

Each retaining hook comprises, in addition to its main part 17a, 17b which carries the hooking tooth with the corresponding coupling hook 6a, 6b, a second part or selection part which is articulated to it around an axis 19a, 19b carried by a lateral ear 20a, 20b (fig. 5), these two ears being oriented towards one another, as shown. The aforementioned second part itself comprises an actuating arm 21a, 21b, a return arm 22a, 22b and a stop heel 23a, 23b. The two actuating arms 21a, 21b are oriented towards one another, their free ends being a short distance from each other between the two shafts 18a, 18b. The two return arms are roughly oriented towards the respective coupling hooks (see FIG. 1) and they are joined together by a return spring 24. Finally, the abutment heels 23a, 23b, roughly oriented in the opposite direction of the return arms, are intended to come to bear under the effect of the spring 24 against the corresponding main part 17a, 17b, in the annular zone thereof which surrounds the shaft 18a, 18b.

It should be noted that in the absence of any external action, the spring 24 maintains the heels 23a, 23b against the main parts 17a, 17b and therefore tends to rotate them around the shafts 18a, 18b in the direction corresponding to the approximation of the attachment teeth (ie destrorsum for 17a and sinistror-sum for 17b).

The main part 17a, 17b of each retaining hook comprises, opposite its hooking tooth, an auxiliary tooth 25a, 25b (fig. 2) with a rectangular profile, which projects relative to the back 26a, 26b of said tooth hanging. In addition to each retaining hook is associated a locking cross bar 27a, 27b common to all the elements of the dobby. When the hook in question is released (upper retaining hook in FIG. 1), its locking bar 27a is applied against its back 26a and against the adjacent lateral flank of its auxiliary tooth 25a, while, when the hook is engaged ( lower hook in Fig. 1), its locking bar 27b bears against the top of the auxiliary tooth 25b. In this case as in the other, the main part of the hook concerned is prevented from rotating under the action of the spring 24 and therefore remains held in position. However, and as will be described in detail below, during the operating cycle of the loom, the bars 27a, 27b momentarily move away from the retaining hooks in the oblique direction indicated by the arrow in FIG. 4 (that is to say roughly parallel to the right lateral flanks of the auxiliary tooth 25a, 25b) so as to release the upper and lower retaining hooks alternately for their selection.

In other words, throughout the dobby, each locking bar 27a, 27b is erased during the selection of the retaining hooks with which it is associated, then it returns to lock them in the position which has been given to them. (position cleared or position engaged).

The locking bars 27a, 27b are preferably controlled by cams, as will be described later with reference to FIG. 8.

Each element of the dobby is associated with a double pusher, comprising a selection head 28 suspended from the upper shaft 18a so as to move in an arc of circle roughly comparable to a straight horizontal line within the limits of its movements, and two flat rods 29a, 29b (one for forward gear, one for reverse gear) whose right ends in fig. 2 are engaged inside the head 28, established in the form of a stirrup, and are articulated thereto around an axis 30 parallel to the shafts 18a, 18b. These rods extend approximately horizontally to the left, their free ends being biased upwards against an abutment crossbar or leveling bar 31 by individual springs 32 attached to the frame of the dobby at 33. It is, d 'somewhere else,

provided with another stop cross member 34 which limits the movement of the heads 28 in the direction of the left under the effect of the actuating arms 21a, 21b when these are free to obey the springs 24. The upper edge of the flat rods 29a, 29b of each pusher 5 is stepped in profile so as to determine a vertical tooth 35a, 35b oriented to the left (therefore opposite the head 28) and which, when the rod has been selected by lifting its end left and rotation around the axis 30, as will be seen later, is actuated by a corresponding tooth-io dante 36a, 36b of a comb 37a, respectively 37b, these two combs being movable back and forth - comes horizontal as will be explained below. Fig. 3 shows that, in the successive elements of the dobby, the rods 29a, 29b are arranged in an inverted manner, so that the same tooth, such as 36a, can i5 correspond to two adjacent rods, such as 29a, which obviously simplifies the production of the combs 37a, 37b. When a rod 29a or 29b is thus moved to the right by the comb which corresponds to it, the head 28 tends to push back the actuating arms 21a, 21b of the second parts of the two retaining hooks 20 of the element considered of the dobby.

The pairs of rods 29a, 29b are guided transversely by the teeth of two fixed combs 38 and 39 (fig. 2 and 3). As for their selection, it is ensured by needles 40a, 40b (fig. 2), each of which is coupled from below to an ear 41a, 41b of the rod 25 considered and which rise to come through a crosspiece 42 playing the role of a perforated guide plate, and from there to feel a strip of perforated paper 43 wound on the passage on a perforated cylinder 44. On the other hand the aforementioned leveling cross member 31 is provided vertically movable to lower the left ends of the rods 29a, 29b with the needles 40a, 40b during each cycle against the springs 32. Depending on the case, the paper can advance in a jerky movement in the conventional way, or on the contrary of a continuous movement, crosses it or platen 42 must then come and go to advance with it and go back 35 during the needle release period, in the known manner.

To simplify the explanations concerning the action of the rods 29a, 29b, we will first of all assume that during a cycle the rod 29a forwards is only moved to the right by the .40 comb 37a which corresponds to it (we will see further on what happens if the reverse rod 29b is also displaced during the cycle and why its displacement remains without effect). The movement of the locking bars 27a, 27b is adjusted so that at this instant one of them has been momentarily brought to the disengaged position for which it releases the main part 17a, 17b from one of the two hooks retaining the element in question, the other bar being in its locked position. Three hypotheses are then to be considered:

1. The main parts 17a, 17b of the two bare reteso hooks are in the erased position of FIG. 2. In this case, and as shown in fig. 4, one of them which is no longer locked by its bar (upper hook) rotates under the effect of its actuating arm 21a; indeed the heel 23a being held against the periphery of the annular zone of the main part 17a by ss the effect of the spring 24, the assembly 17a, 21a behaves like a single rigid part driven in rotation by the head 28 to the 'against the return action of the spring 24. The main part 17a thus arrives at the engaged position to which it is then locked by the bar 27a which returns to its rest position (fig. 5). 60 The dobby is adjusted so that this occurs at the moment when the corresponding towing hook 6a ends its recoil stroke so that the two hooks hang on to each other and are locked in the hooked position . As for the main part 17b of the other retaining hook, as it is locked by its 65 bar 27b it cannot follow its actuating arm and remains in the retracted position (fig. 5), its second part 21b, 22b, 23b simply rotating around the axis 19b against the spring 24. Due to the engagement of one of the retaining hooks, the balance 4 does not

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can no longer oscillate freely and, consequently, the frame or group of frames controlled by the connecting rod 3 of FIG. 1 will be raised.

2. The main part I7a of the retaining hook, the locking bar of which has been brought into the erased position, is itself also in the erased position, but the main part 17b of the other hook is locked in the engaged position. In this case, the first hook is brought to the engaged position as explained above. The balance 4 is then retained in the advanced position without being able to oscillate, so that the frame or group of frames controlled by the dobby element considered remains in the raised position.

3. The main part I7a of the retaining hook whose locking bar 27a is deleted is in the engaged position. In this case, this main part 17a is held in the engaged position by the effect of the head 28 on the actuating arm 21a and of the stop of the heel 23a against the periphery of the annular zone of said part 17a as explained above. As for the main part 17b of the other retaining hook, due to the locking action of the bar 27b, it remains in the position in which it is located.

Of course, if the pusher is not actuated, the retaining hook such as 17a, released by its bar 27a, remains in the disengaged position, if it was already there, or passes to this disengaged position, if was on the contrary engaged.

Thus, the single spring 24 ensures:

- The return of the heels 23a, 23b against the annular zones of the main parts 17a, 17b of the retaining hooks;

- bringing one of the main parts 17a, 17b to the engaged position after a bar 27a, 27b has retracted when the actuating arms are pushed back by the head 28, owing to the fact that the heel 23a, 23b remains applied against the aforementioned annular zone;

- The return of the main part 17a, 17b to the erased position when it is released by its locking bar and when the pusher head is not advanced by the combs;

- the return to the left of the head 28 against the cross member 34.

It also allows the displacement of the second part of each hook relative to the first when necessary.

The movements of the locking bars 27a, 27b of the leveling bar 31 and of the combs 37a, 37b are preferably controlled by desmodromic cams. There is shown by way of example in FIG. 6 the mechanism which corresponds to the aforementioned combs, it being understood that similar mechanisms can be used for the various bars. In this figure, we see at 45 a disc wedged on the shaft 46 of the dobby or on a tree connected to the latter. In one of the faces of this disc, a groove 47 has been dug which desmodromically actuates two rollers 48a, 48b respectively carried by double levers 49a, 49b mounted on fixed pivots 50a, 50b and the opposite ends of which are properly coupled to the two combs. As regards the comb 37a for forward travel, this coupling is effected by means of a groove and stud system while, for the comb 37b for reverse travel, a connecting rod 51 is provided. As shown, the profile of the groove 47 is symmetrical, but the rollers 48a, 48b are offset there relative to each other, so that their cycles of movement are out of phase and the same applies to the combs (see plots 37a and 37b in fig. 8).

Of course, these combs, as well as the locking bars 27a, 27b and the cross member or leveling bar 31, are suitably guided in the frame of the dobby.

Fig. 7 indicates a variant of the rod selection control 29a, 29b of the pushers. Here we find the return springs 32 attached to the cross member 42, as well as the cross member or leveling bar 31. But the selective vertical displacement of the left end of said rods is obtained by means of electromagnets 52a, 52b whose cores mobiles are harnessed to them by wires 53a, 53b. We see at 54a corresponding fixed counter-cores carried by a cross member 55. An appropriate system selectively sends current to the electromagnets when the leveling cross member is lowered, so that, when the latter is raised, the rods corresponding to the excited electromagnets remain in the lowered position. Note that these are staggered on the cross member 55 to reduce the width of the assembly.

The selective sending of current to the electromagnets can be carried out by any means known in the art of electrically controlled armor mechanics.

Of course, if the electromagnets are strong enough, the leveling bar can be omitted, the magnetic attraction sufficient to selectively lower the rods.

Fig. 8 shows the movements of the various essential organs of the dobby and makes it possible to understand how, although the reverse rods 29b are never put out of action, they do not intervene during the forward movement, while, likewise, those 29a forward do not intervene either when you rotate the dobby in reverse. In this figure for forward travel, the tracks should be read from left to right and vice versa for reverse travel. The locking bars 27a, 27b move between the locked position and the unlocked position. When a comb 37a, 37b advances, it actuates the selected rods and, when it moves back, it releases them for the next selection. The penultimate trace corresponds to the advance of the paper 43 when the cylinder 44 rotates in successive jerks, the crosspiece or plate 42 remaining fixed, while the last relates to the case of a continuous rotation of the cylinder, the plate following d 'first the paper, then backing down during the lowering of the needles to shift a step or feel around it.

To simplify the explanations, it has been assumed that only two frames I and II were provided, making a simple taffeta weave. As the first layout shows, these two frames then oscillate with a 180 ° phase shift. The locking bar 27a moves back each time the frame I reaches the low position and advances as soon as it rises. Its movement is centered in relation to that of the frames. The bar 27b performs an identical movement, but with a phase shift of 180 ° so as to correspond to the low positions of frame II or high positions of frame I. The comb 37a of forward movement advances as soon as one or the other of the bars 27a, 27b is completely pushed back, then it moves back as soon as it has fully returned to the advanced (locked) position. Therefore, its movement is slightly out of phase late (therefore to the right) compared to that of the aforementioned bars. The reverse comb 37b performs exactly the same movement, but following the graph from right to left and no longer from left to right, so that its movement is out of phase in advance (to the left). It is moreover clearly seen that the movements of the two combs are symmetrical with respect to the perpendicular bisector of the horizontal segment which corresponds to the retracted or unlocked position of said bars. The movements of the combs add up in a way to activate the head 28 which, if we read the graphic from left to right (forward), is first advanced by the comb 37b (and of course the rod 29a), then begins to move back with this comb, but is advanced again by the comb 37a. As for the crossbar or leveling bar 31, its lowering times are centered with respect to the crossing points of the frames (or more exactly lines which represent their movements). It is easy to see that these times appear when the locking bars are in the advanced (locked) position and that the combs are on the contrary in the retracted position.

However, it should be noted that, if you are in forward gear (reading the graph from left to right), the reverse comb 37b returns to its retracted position (without action on the rods 29b) while the either of the locking bars 27a, 27b is still in the retracted position. As a result, if this comb has advanced the rod 29b, which may have acted on an actuating arm 21a, 21b via the head 28, this arm has already returned to its previous position when the bar

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corresponding lock advance. So the selection that this rod 29b was able to make is only transitory and does not remain. From which it is concluded that, during the forward movement, the comb 37b and the rods 29b have no action on the dobby or, in other words, that they operate empty.

Of course, if we consider the case of reverse gear, that is to say if we follow the graph in FIG. 8 going from right to left, one arrives at an exactly opposite conclusion from the previous one, namely, that during this reverse gear, the forward driving rods 29a have completely retracted before the locking bars advance, so that these rods and the corresponding comb 37a again operate empty.

Under these conditions, it suffices that the two groups of needles 40a and 40b are guided in the crosspiece or plate 42 so that their feeler areas on the paper 43 are offset by two picks (a drop and a lift of one frame) so that, from the start of reverse gear, the corresponding 40a feel the perforations representative of the blow already made in forward gear.

Of course, nothing prevents the paper from having two series of perforations, one for forward gear, one for 5 reverse gear, in which case all the needles can be on the same line.

In any case, the invention makes it possible to provide for each element and for each direction of travel only one actuating member (head 28) of the actuating arms 21a, 21b of the retaining hooks, which considerably simplifies the dobby. In addition, the rods 29a, 29b cannot flex significantly in the vertical direction, while they are retained in the transverse direction, which excludes any vibration liable to cause a selection error. Finally, each element comprises only a single spring exerting a significant effort, namely the spring 24 (the springs 32 being very light), which considerably reduces the risks of malfunction caused by the weakening or breaking of a recall organ.

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Claims (9)

622,039 2 1. Double dobby dobby for weaving looms, in which each element associated with a hoop frame or group of heddle frames comprises a half-pendulum driven back and forth, a balance carried at articulation by it ci and whose ends are equipped with coupling hooks, this balance being actuated by two crosspieces carried by oscillating supports and common to all the elements of the dobby, and two retaining hooks intended to cooperate selectively with the coupling hooks , each of these retaining hooks comprising, on the one hand, a first part or main part articulated to the frame and which carries the hooking spout, on the other hand, a second part or selection part articulated to the first, connected to this by a spring and stop system, and receiving the action of the armor mechanism, the whole so that this mechanism can prepare the selection of the balance considered by moving the second part of one of the hooks to re held before the corresponding towing hook has come to the end of the recoil stroke, this retaining hook disappearing in the manner of a pawl when said towing hook passes to hang behind it, while '' to each of the two rows of dobby retaining hooks is associated a locking bar driven back and forth and which cooperates with the first part of each hook of the row considered to lock this part either the erased position for which the retaining hook in question cannot retain the corresponding towing hook, that is to say on the contrary to the engaged position for which this first part clings to said towing hook, which bars alternately release the first parts of the hooks of restraint during selection, one during even strokes, the other during odd strokes, characterized in that, in each element, the second parts or selection parts (21, 22, 23) of the d the retaining hooks are activated during selection by a single member (28, 29) associated with the armor mechanism (31, 40, 43). 2. Dobby according to claim 1, characterized in that the single actuating member of the second parts (21,22,23) of the two retaining hooks of each element is constituted by a pusher (28, 29). 3. Dobby according to claim 1, characterized in that the single actuating member of the second parts (21, 22, 23) of the two retaining hooks of each element receives the armor mechanism (31, 40,43) a stress corresponding to the normal forward movement of the dobby and another stress corresponding to the reverse of the latter, these two stresses being offset so that, for each step, that corresponding to the other stops while the bars of lock (27) are still in the unlocked position. 4. Dobby according to claim 1, characterized in that each pusher comprises a head (28) capable of coming into contact with the second parts (21, 22, 23) of the two element retaining hooks and at least one rod ( 29) whose axis is arranged in the plane of symmetry of the two rows of dobby retaining hooks, this rod being able to be moved somewhat perpendicularly to this plane by the armor mechanism (31, 40, 44) to receive or not the action of a member (37) driven by a back and forth movement in synchronism with the operation of the dobby. 5. Dobby according to claim 4, characterized in that the rod (29) comprises a lateral tooth (35) adapted to cooperate with a corresponding tooth of a transverse actuating member (37) common to several elements of the dobby and movable back and forth parallel to the plane of symmetry of the two rows of retaining hooks. 6. Dobby according to claims 3 and 4, characterized in that at the head (28) of each pusher are articulated two flat rods (29) juxtaposed and corresponding respectively to normal forward and reverse, these two rods capable of receiving, independently of one another, the action of two members (37) animated back and forth suitably out of phase with respect to each other, while means are provided to positively guide the movement of the head and the ends of the rods which are articulated to it. 7. Dobby according to claim 6, characterized in that the two actuating members (37) are constituted by nested combs, the order of the rods (29) being reversed in the transverse direction in the successive elements, so that the tooth (36) of one of these combs can act both on two rods (29) belonging respectively to one and to the other of the two neighboring elements and corresponding to the same direction of travel. 8. Dobby according to claim 1, characterized in that the second part or selection part (21, 22, 23) of each retaining hook is articulated to the first part or main part (17) about an axis (19 ) offset towards the plane of symmetry of the two rows of retaining hooks with respect to the axis of oscillation (18) of the first part, the second parts of the two retaining hooks of the same element being connected one to the other by a single spring (24) which, on the one hand, tends to return each second part to its position of abutment against the first part to which it is articulated and, on the other hand, when the two parts are in abutment, tends to recall the whole of the retaining hook towards its released position, always allowing the second part to move against the return action of the spring when it is requested by the single actuation (28) and that the first part (17) to which it is articulated is ver rusted by a locking bar (27). 9. Dobby according to claim 4, with an armor mechanism comprising reading needles feeling a strip of perforated paper, characterized in that these needles (40) are directly coupled to the rods (29) of the pushers, means (32, respectively 31) being provided to urge the needles towards the paper (43) during a selection phase and to separate them between two successive selection phases. Double dobby dobbies are known for weaving looms in which each of the ends of the balance corresponding to a frame or group of frames from the loom includes a towing hook capable of cooperating with a retaining hook itself comprising on the one hand, a first part articulated to the frame and which carries the hooking spout, on the other hand, a second part articulated to the previous one, connected to the latter by a spring and stop system, and receiving the action of the armor mechanism, the whole so that this mechanism can prepare the selection of the balance considered by moving the aforementioned second part of one of the retaining hooks before the corresponding coupling hook has come to the end of its travel backward, this retaining hook disappearing in the manner of a pawl when said coupling hook passes to come and hang behind it. In known dobbies of this type, the armor mechanism acting on the second parts of the retaining hooks can be arbitrary. It is in particular possible to attach to these second parts of the needles working either in traction or in pushing, and which can either directly feel the perforated paper, the aforementioned second parts being driven back and forth by an appropriate device , for example eccentric, or receive the action of a train of bars with double back-and-forth movement, the selection then being made by means of reading needles which feel the paper in the well known manner in Verdol mechanics. For each element of the dobby, that is to say for each of the scales thereof, it is necessary to provide two needles corresponding respectively to one and to the other of the retaining hooks associated with the element considered and the perforated paper must 5 10 15 20 25 30 35 40 45 50 55 60 65 3 622,039 have two rows of perforations. If, on the other hand, the dobby must operate in reverse, two needles are required for each hook, therefore a total of four per element, or else auxiliary devices for moving the needles relative to the perforated paper must be provided. All this complicates the dobby. In addition, the needles may vibrate at high speeds causing selection errors. Finally, one must provide for each retaining hook a return spring of the first part of this hook to its rest position and a return spring of the second part to its position of abutment against the first part, these springs in front be properly tared against each other, which multiplies the possible causes of faulty operation. In these known dobbies, a more positive and safer operation has been ensured by providing two reciprocating locking bars which block the first parts of the retaining hooks and all the elements either in the engaged position or at the erased position, thus avoiding unwanted engagement or disengagement, but operational safety nevertheless remains linked to the correct setting of the return springs and the presence of these bars does not simplify the armor mechanism.